A lithography method has been generally employed as a production method of a semiconductor circuit device. In the case where a semiconductor circuit device is produced by the lithography method, a conductor thin film layer, such as a metal film, used as a conductor wiring material, and an interlayer insulating film, such as a silicon oxide film, for insulating among the conductor thin film layers and the wiring are formed on a semiconductor substrate, such as a silicon wafer. Thereafter, a photoresist is coated uniformly on the surface thereof to provide a photosensitive layer, which is then subjected to selective exposure and development, thereby forming a desired resist pattern. The thin films in the lower layer part are subjected to a selective etching treatment with the resist pattern as a mask, thereby forming a desired wiring pattern on the thin films, and then the resist pattern used as a mask is removed, whereby the semiconductor circuit device is produced.
The increase in integration degree of a semiconductor circuit device requires miniaturization in dimensions of patterning process. Associated thereto, a dry etching method using etching gas is becoming mainstream for the aforementioned selective etching treatment. An alloy containing aluminum as a major component, which has been used as the circuit wiring and the electrode material, has a resistance that is too high for the wiring material of the highly integrated semiconductor circuit device, and there may be problems, such as decrease in response speed due to wiring delay, increase in generated heat amount, and electromigration due to increase in electric current density. For solving the problems, a wiring material using copper or an alloy containing 80% by mass or more of copper (which will be hereinafter referred to as a copper wiring material), which has a small electric resistance and is excellent in migration characteristics as compared to the alloy containing aluminum as a major component, is being widely developed and employed.
However, there are problems that copper useful as a wiring material is difficult to be subjected to the selective etching by the dry etching method using etching gas, and upon making in contact with an insulating material, such as an interlayer insulating film, copper in a copper wiring material is diffused into the insulating material, thereby impairing the insulating property thereof. Furthermore, the copper wiring material is liable to be oxidized to form an oxide on the surface thereof, and is liable to be corroded in an aqueous solution on wet etching, rinsing or the like, and thus the copper wiring material is necessarily handled with care.
In the case where copper or a copper alloy containing 80% by mass or more of copper is used as a wiring material, it is necessary to use a wiring formation technique that does not employ a dry etching method using etching gas. Accordingly, a wiring formation technique referred to as a damascene method is employed, in which a trench in the form of the wiring is formed in an interlayer insulating film, in which a metal, such as a copper wiring material, is filled therein.
For preventing diffusion of copper in the copper wiring material into the insulating material, which lowers the insulating property thereof, a procedure is necessarily employed in that the copper wiring is covered with a film that prevents copper from being diffused (which will be hereinafter referred to as a diffusion preventing film). The diffusion preventing film is disposed between the copper wiring material and the insulating material in view of the function thereof. Examples of the formation method therefor employed include a method, in which an insulating material, such as an interlayer insulating film, having been formed into a desired shape is covered with a diffusion preventing film, which is generally referred to as a barrier layer or a barrier metal, formed by a film formation method, such as a sputtering method and a CVD method (a chemical vapor deposition method), and then a copper wiring material is formed thereon, and a method, in which a copper wiring material is formed on a semiconductor substrate by a plating method, and then flattened by a chemical mechanical polishing method (which will be hereinafter referred to as a CMP method) for removing an excessive copper wiring material and flattening the surface of the copper wiring, and then the copper wiring is covered with a diffusion preventing film, which is generally referred to as a cap layer, i.e., a cap metal, formed by a sputtering method, a CVD method or the like. In any of these methods, the diffusion preventing film is formed and is in contact with the surface of the copper wiring material. The copper wiring material that is to be covered with the diffusion preventing film, which is referred to as a barrier layer, a barrier metal, a cap layer or a cap metal, is in an exposed state before covering with the diffusion preventing film. The copper in the exposed state is easily oxidized with oxygen in the air, and an oxide layer is formed on the surface of the copper wiring material before covering with the diffusion preventing film. While depending on the waiting time until the step of forming the diffusion preventing film, the exposed surface of the copper wiring material may be considerably oxidized to form foreign matters, or may suffer formation of contamination, corrosion and foreign matters derived from the production environment. Upon limiting the waiting time until the step of forming the diffusion preventing film for avoiding the problems, disadvantages on productivity and economy may occur due to complicated procedures.
Specific examples of the step where the surface of the copper wiring material is exposed include a wiring formation step by the damascene method, in which an interlayer insulating film or a diffusion preventing film is etched to form a trench in the form of the wiring, and a copper wiring material is then filled in the trench. Examples of the cases where the surface of the copper wiring material is exposed in the step include the following cases (1) and (2).
(1) The surface of the lower layer copper wiring material is exposed in the step, in which an interlayer insulating film or a diffusion preventing film (a cap metal) is etched to reach the copper wiring material as the lower layer for achieving electric conduction.
(2) After forming by a plating method a diffusion preventing film (a barrier metal) or a copper wiring material in the trench in the form of the wiring formed in the case (1), the surface of the copper wiring material is exposed in the step of flattening by a CMP method.
The cases (1) and (2) include a cleaning step with a cleaning liquid, a rinsing step with extra pure water and a drying step, and in these steps, changes and modifications of the state of the surface of the copper wiring material, i.e., oxidation and corrosion of the surface of the copper wiring material, may occur.
Specifically, in the case where a dry etching process is used in the step of etching the interlayer insulating film for forming the trench in the form of the wiring, i.e., the case (1), a residue derived from the dry etching gas, the resist, the film to be processed, the materials of the members inside the dry etching chamber, and the like (which will be hereinafter referred to as an etching residue) is formed. The etching residue existing is not preferred since it causes such phenomena as an increased resistance, an electric short circuit, and the like. For removing the etching residue, in general, there is such a process that the surface is cleaned with a cleaning liquid, and immediately after cleaning, the cleaning liquid is rinsed out with an organic solvent or extra pure water. In the case where the cleaning liquid exhibits alkalinity, it may be rinsed with carbonated water for neutralizing the alkalinity. In the case of a cleaning step by a spin spraying method achieved with a single substrate cleaning device or the like, the rinsing step may be performed with carbonated water instead of extra pure water for preventing static charge of the semiconductor substrate.
In the process where a copper wiring material is formed by a plating method, and then the surface thereof is flattened by CMP, i.e., the case (2), the surface of the copper wiring material formed by a plating method is polished with a slurry containing polishing particles, such as cerium oxide, and a polishing pad (i.e., the CMP process) for providing the desired thickness, flatness and wiring pattern, and then excessive copper thus ground, the polishing particles remaining on the surface of the copper wiring material thus polished, and the like are removed by cleaning. The cleaning process includes a rinsing step with extra pure water or carbonated water. Not only carbonated water, but also extra pure water in this case easily exhibit weak acidity through absorption of carbon dioxide in the air. The rinsing with the weakly acidic water easily corrodes the surface of the copper wiring material. In the drying step after rinsing, such methods are employed as a method of spinning the semiconductor substrate for draining water and drying, blowing air onto the spinning semiconductor substrate for draining water and drying, and a method of drying the substrate with hot air or steam, but there are cases where the surface of the copper wiring material is oxidized or modified in the drying step depending on the drying method. Even when the surface of the copper wiring material can be prevented from being oxidized or modified in the drying step, the surface of the copper wiring material is exposed until the subsequent step of forming a diffusion preventing film, and may be easily oxidized with oxygen in the air, thereby forming an oxide layer on the surface of the copper wiring material. The surface of the copper wiring material may be considerably oxidized to form foreign matters, or may suffer formation of contamination, corrosion and foreign matters derived from the production environment.
The copper wiring material thus modified through corrosion or oxidation is not desirable since it may cause increase in electric resistance, decrease in adhesion to the diffusion preventing film, occurrence of voids, and the like. With the progress of miniaturization in recent years, slight modification, e.g., minute corrosion, minute increase in thickness of the oxide film, and minute foreign matters, that has been permitted may cause great influence on the performance of the semiconductor device, which brings about a significant problem of defective products. For avoiding the problem of defective products, it is important to maintain clean the surface state of copper or a copper alloy containing 80% by mass or more of copper, which will be a wiring material.
In the case involving the problem of modification, such as oxidation, corrosion and foreign matters, on the surface of the copper wiring material in the cleaning step as described above, a metal modification preventing method has been known that a deoxidizing agent removing dissolved oxygen, a corrosion preventing agent, a passive film forming agent or the like is used in the water rinsing step. It has been also known in the drying step that a vacuum drying method or a drying method performed in a nitrogen atmosphere is employed for preventing modification on the surface of copper. While examples of the deoxidizing agent used for removing dissolved oxygen in the water rinsing step include a reducing agent, such as hydrazine, hydroxylamine, sodium sulfite and a sodium bisulfite, the deoxidizing agent can prevent the surface of the copper wiring material from being oxidized or modified in water upon rinsing with water, but fails to prevent completely the surface of the copper wiring material from being oxidized or modified upon drying and, after drying. Furthermore, oxidation or modification on the surface of the copper wiring material is difficult to be avoided by employing a vacuum drying method or a drying method performed in a nitrogen atmosphere in the drying step unless the surface of the copper wiring material is not exposed, and moreover, a vacuum drying method and a drying method performed in a nitrogen atmosphere require high cost for equipments with low workability and are disadvantageous in cost due to nitrogen used in a large amount.
As a copper surface protective film, Patent Documents 1 to 3 disclose a pre-drying treating liquid containing acetylene alcohol with a hydroxylamine compound, a hydrazine compound or an alkylalcohol, and disclose that a metal surface free of unevenness and stain (discoloration) is obtained by suppressing oxidation in a drying step. However, some kinds of metals are easily oxidized, and problems may occur in prevention of corrosion on rinsing with pure water exhibiting weak acidity used in a production process of a semiconductor circuit device, and a surface of a copper wiring material exposed during a waiting time from a drying step to a subsequent step.
Patent Documents 4 to 6 propose the use of an acetylene alcohol compound, an acetylene diol compound, and ethylene oxide or propylene oxide thereof mixed in an organic acid, and a developer liquid, a separating liquid, a cleaning liquid and a rinsing liquid therefor, or a CMP slurry used in a production process of a semiconductor. However, they cannot prevent occurrence of contamination, corrosion and foreign matters derived from the production environment, formed on the surface of the copper wiring material in the production process of a semiconductor circuit device or the like.
Furthermore, for preventing failure of a semiconductor device caused by oxidation or modification of an exposed copper surface, there is a method for suppressing oxidation or modification of the copper surface by preventing the metal from being in contact with the air (e.g., oxygen) with a modification preventing agent or an anticorrosion agent attached to the copper surface. Patent Document 4 discloses as conventional art the use of benzotriazole (which will be hereinafter abbreviated as BTA) as an anticorrosion agent for copper in a photoresist separating liquid used in a production process of a semiconductor circuit device containing copper wiring. The use of an amine compound or a triazole compound, such as BTA, forms a complex compound of the compound with copper on the surface of copper, thereby failing to provide a clean copper surface. The anticorrosion agent present on the copper surface is not desirable since it may cause increase in electric resistance, decrease in adhesion to the diffusion preventing film, occurrence of voids, and the like, as similar to modified copper. A triazole compound or the like with low solubility in water is not desirable since the compound remains on the wafer surface even after rinsing with water and is difficult to be removed, thereby providing adverse affect on the subsequent process. Moreover, a triazole compound, such as BTA, is poor in biodegradability and thus provide a large load on waste liquid processing.
As described hereinabove, it is significantly important that for producing a highly integrated and highly miniaturized semiconductor circuit device with high accuracy and high quality, it is important to form a diffusion preventing film while maintaining a clean surface of a copper wiring material. Accordingly such a technique is demanded that in production of a semiconductor circuit device, a surface of a copper wiring material is protected from modification, such as corrosion and oxidation, and contamination derived from the production environment, thereby maintaining the surface clean during the period of from a step of exposing the surface of the copper wiring material, e.g., a step of forming a trench in the form of wiring reaching the lower layer copper wiring material in an interlayer insulating film to expose the surface of the copper wiring material, and a step of flattening by CMP a surface of copper or a copper alloy formed by a plating method to expose the surface of the copper wiring material, to a step of forming a diffusion preventing film.